{"id":395731,"date":"2024-06-29T12:23:33","date_gmt":"2024-06-29T12:23:33","guid":{"rendered":"http:\/\/savepearlharbor.com\/?p=395731"},"modified":"-0001-11-30T00:00:00","modified_gmt":"-0001-11-29T21:00:00","slug":"","status":"publish","type":"post","link":"https:\/\/savepearlharbor.com\/?p=395731","title":{"rendered":"Confusing extensions in Swift<\/span>"},"content":{"rendered":"
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This post is a little bit the information aggregator. If you find a mistake, you could write to me about it I really appreciate that. Have a nice read.<\/p>\n

Example with JSONDecoder<\/h2>\n

What would happen if we run the following piece of code?<\/p>\n

struct Test<T>: Codable where T: Codable {     enum CodingKeys: String, CodingKey {         case value     }          let value: T     let info: String }  extension Test {     init(from decoder: Decoder) throws {         let container = try decoder.container(keyedBy: CodingKeys.self)         self.value = try container.decode(T.self, forKey: .value)         self.info = \"Default init(from decoder:)\"     } }  extension Test where T == String {     init(from decoder: Decoder) throws {         let container = try decoder.container(keyedBy: CodingKeys.self)         self.value = try container.decode(T.self, forKey: .value)         self.info = \"Custom init(from decoder:)\"     } }  let data = #\"{\"value\":\"Hello, World!\"}\"#.data(using: .utf8)! let object = try? JSONDecoder().decode(Test<String>.self, from: data) print(object.debugDescription) <\/code><\/pre>\n
  Try thinking for 5 seconds about the result.<\/p>\n
                         The result<\/b>                         <\/p>\n
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Optional(     Test<String>(         value: \"Hello, World!\",          info: \"Default init(from decoder:)\"     ) ) <\/code><\/pre>\n
  <\/div>\n<\/p><\/div>\n
  <\/a>  <\/p>\n
Why did it happen?<\/h2>\n
  The JSONDecoder:decode<\/code> definition looks like<\/p>\n
func decode<T>(_ type: T.Type, from data: Data) throws -> T where T: Decodable<\/code><\/pre>\n
  We see the generic function<\/code> and also the metatype T.Type<\/code>. I\u2019m not focusing your attention on those two definitions by accident. We should understand these structures of language.<\/p>\n
  You could read more about metatypes:<\/p>\n